8bit computer

[Prof_Magnesium]

I would like to know if it is reasonable to attempt to simulate an old 8bit computer with Logic Circuit. It would be based on a 8080 microprocessor with a 48kb RAM and a 24kb ROM.

[admin]

It is reasonable. You can look around in this forum or samples and you will find quite a few computers people built.

[Xaetral]

yup, I was very impressed by how fast this software runs, it can run my 8bits risc processor + a small GPU at 2kHz on a bad laptop (and 20kHz on i7-7700k)

[Prof_Magnesium]

So I see that it is not impossible! I have the list of the CIs used in this computer. I started to search for those already programmed by Logic Circuit and I have found a lot. But there are some I did not found. Here is the list:

TTL
74LS122 Retriggerable monostable multivibrator
74LS123 Dual Retriggerable monostable multivibrator
74LS155 Dual 2-Line to 4-Line Decoders/Demultiplexers with totem-pole ouput
74LS164: 8-bit parallel-out serial shift register
74LS165: 8-Bit Parallel-to-Serial Shift Register
74LS170: 4 X 4 register file with open-collector outputs
74LS193: Presettable 4-bit binary up/down counter
74LS241: Octal buffer/line driver with 3-state outputs
74LS251: 8-input multiplexer with 3-state outputs
74LS253: Dual 4-input multiplexer with 3-state outputs
74LS257: Quad 2-input multiplexer with 3-state outputs
74LS393: Dual 4-stage binary counter

ROM
74S287N, 2111: (256 x 4) 1024-bit TTL PROM
74S288, 82S23A-82S123A: (32 x 8) 256-bit TTL PROM
uPD2364, MK36000: Read only memory 8192 words, 8 bits/word

RAM
4116, uPD416: 16,384 x 1 bit dynamic RAM
INS8154: N-channel 128-by-8 bit RAM input/output (RAM I/O)

Microprocessor and peripherals
8080A: 8-bit N-channel microprocessor
uPB8224: Clock generator and driver for 8080A CPU
TMS5501: Multifunction input/output controller
D8253C: Programmable interval timer
D8255A: Programmable peripheral interface
AM9511, i8231a: Arithmetic processing unit

I will try to program them but if some were already programmed, I would be happy to use their design!

I read that Logic Circuit would not be able to program monostable multivibrator. Could you confirm this fact?

With my best regards,

Prof. Magnesium

[Xaetral]

Well, you are trying to make an electronic circuit on a logical simulator, so you can't just plug pre-made things like IRL ( 'w')

[admin]

The program is for emulating logical circuits only. So anything with transistors or specific chips that commercially or otherwise available is out of the scope.
However there is a tri state gates are available, and there is a clock gate too. So you can use clock instead of your multivibrators.
There is a memory components you can use both ROM and RAM.
You can find some multiplexers, decoders registers in the samples and projects on this forum.

[Prof_Magnesium]

Thank you very much for these advices. I started to work on this 8-bit computer project and I have already published some CIs I have made, in Circuit Talk "My first circuit: 74155". Between them, there are the 74122 and 74123 on-shots. I also looked at ROM and RAM. I have found it is very easy to use.

Now I have a doubt: how many logical elements can I reasonably put in my project? 100? 1000? more? Other questions: the clock I put in a one-shot IC is autonomous? Can I control its frequency? How is defined the velocity (frequency) of the simulation?

With my best regards, Prof_Magnesium.

[admin]

Hi Prof_Magnesium,
There is no any restriction on number of elements.
All clocks are running pretty much as one. You can change frequency when power is on. There is slider and checkbox in the left bottom corner in the application window.
Regards,
Eugene

[Xaetral]

most of the projects made on this software don't exceed 10k logic gates but you can still run them above 2kHz